Dynamic binding is a topic that seems key in Service Oriented Architectures, since it provides a form of decoupling between service requesters and service providers. The idea is that the service requester is dynamically bound to the service endpoint.

Dynamic binding can take many forms:

1. The data upon which the binding takes place can vary.
a. In the most simple form the logical name of the service is translated to the physical address of the service endpoint.
b. A more elaborate form is content-_base_d routing: _base_d upon the contents of the service invocation message the service endpoint is determined.
c. Another form is policy-_base_d routing, where the Quality of Service required by the service requester is the criterion _base_d upon which a service endpoint is selected.

2. The component that performs the binding can vary: either the service requester or an intermediary.
a. In case the service requester performs the dynamic binding, it actively queries a service registry, selects the appropriate endpoint and invokes the service.
b. If an intermediary such as a message broker performs the dynamic binding, the service requester only needs to send the message to the intermediary.

3. The technology used for the service registry can vary.
a. You can build your own lookup table with mappings from logical names to physical addresses.
b. You can using the naming service provided by the implementation technology such as JNDI in a Java environment.
c. You can use a UDDI.
d. You can use some other registry product.

It would be a good idea to start sharing experiences with respect to dynamic binding. Do you use dynamic binding? Which of the forms of dynamic binding do you use? What are best practices? What have we learned so far?

My experience is that organisations are not very often have very simple dynamic binding mechanisms in place, or do not use dynamic binding at all. An example of the latter is where WSDL files are put on a central web server and binding takes place during development. My current client performs dynamic binding in a message broker, that uses a custom lookup table to map technical service names to service endpoints which are all provided through WebSphere MQ. Also, the content-_base_d routing facilities of the message broker are used.

Regards,
Danny Greefhorst